Wideband 4 × 4 Butler Matrix in the Printed Ridge Gap Waveguide Technology for Millimeter-Wave Applications

Abstract

A wideband printed ridge gap waveguide $4\times 4$ Butler matrix at 30 GHz is presented. The printed ridge gap technology is used as it has very low losses and supports the propagation of quasi-TEM mode. Each component of the Butler matrix has been designed and analyzed where a superior performance is achieved in terms of bandwidth and size. The designed components are combined to form the Butler matrix. The Butler matrix has a wideband performance where the return loss and isolation levels are higher than 10 dB in the frequency range from 26.9 to 33.3 GHz, the output amplitude imbalance is ±1.6 dB, and the phase error is ±10°. The measured radiation patterns are in a good agreement with the simulated ones, beam directions are at ±13° and ±36° at the center frequency. The gain is ranging from 10.2 to 11.35 dBi for excitation from port 1 and ranging from 8.4 to 10.2 dBi for excitation from port 2.